Geologic Timeline Individual Reflection

3 of the major events of Earth's history include the Cambrian Explosion, the Permian Extinction, and the Cretaceous extinction. The Cambrian Explosion was highly significant and is often referred to as the most significant evolutionary event on Earth due to the rapid appearance of many animals with mineralized, fossilized remains. The evolution of skeletal structures that leave behind fossils is essential to the study of fossils. The Permian Extinction is highly significant because it was the largest extinction event in all of Earth's history, with 96% of all marine species becoming extinct. The Cretaceous extinction is also very significant because without the extinction of the dinosaurs, mammals would have never radiated and humans would have never came to be.

Earth's history relative to human history is much more grand than I had first expected. On the timeline extending from one end of the classroom to the other, our little sliver of time is absolutely negligible.

However, despite this short period of time that humans have been on this planet, they have had massive effects. Ice caps are melting, many places are flooding, nature all around us is being destroyed and used instead for industry. At this rate, I feel that the human population will not be able to sustain itself for much longer until we choke ourselves to death.

One question I wonder about is why it took so long for humans to evolve, to come to be. So much of Earth's history involved only single-celled organisms, which seems a bit counterintuitive as multicellular organisms seem more likely to dominate.

Below I have attached a couple photos of the timeline:
 

Unit 8 Reflection

I always like to start off with the title of the unit. This unit was called Constant Change. This makes a lot of sense because evolution is all about how populations are always changing. 

But how exactly does evolution work? There are many mechanics involved in evolution, but one of the main causes is natural selection. In order for natural selection to occur within a population, there must first be variation. Variation is created through mutations and sexual reproduction. Natural selection favors individuals with traits that help them survive better, causing them to better produce more offspring, so that over time, the population begins to look more like these individuals. An interesting lab we did to demonstrate this concept was the hunger games lab. Other factors that can cause evolution include gene flow, genetic drift, sexual selection, and mutations. 

Speciation is one of the causes of evolution. As two populations of the same species have reproductive isolation, they begin to evolve differently based on their different ecological niches. Soon, they become so different that they can no longer reproduce with each other anymore. This is when one species becomes two. 

There is a lot of evidence to back these ideas up. First and most obvious is fossils. Fossils found in the earth can tell scientists a lot about when and what individuals looked like. By carefully studying the differences from fossil to fossil, it is pretty clear how and when a population evolved. Also good evidence is the fact that many organisms that are very different (i.e. birds and flies) can evolve analogous and homologous structures. 

One thing that I wonder a lot about is that although it appears that many populations of organisms like animals and plants are evolving, I feel that the human population appears to be still quite the same as before. Why is that? Hmmm.

Below, I have attached some images that I feel highlight some of the key ideas of this unit: